Slurry explosives and emulsion explosives are typical of the conventional hydrous explosives. In these explosives, the active explosive components comprising an oxidizer solution, an inflammable material and a sensitizer and the bubbles are held stably in high concentrations in a mass in the presence of a sizing agent, and these explosives are usually detonated by means of a detonator. In the slurry explosives, the aerated bubbles or chemical bubbles are usually allowed to exist in the explosive composition to let them play a role like a sensitizer, and guar gum is used as sizing agent to compose an aqueous gel. In the emulsion explosives, an oxidizer solution and an oil serving as an inflammable agent are combined to form a W/O type emulsion in the presence of a surfactant serving as a sizing agent. The bubbles in these explosives comprise glass or resinous microballoons, besides the aerated bubbles.
Use of hollow monocellular thermoplastic particles for the improvement of detonation or the adjustment of density of these explosives is mentioned in U.S. Pat. No. 3,773,573 and JP-A-54-92614 with reference to slurry explosives and in JP-A-56-100192 and JP-A-59-78994 with reference to emulsion explosives. In U.S. Pat. No. 3,773,573 is disclosed a technique for application of hollow monocellular thermoplastic particles to a wide variety of explosives including slurry explosives, according to which the explosive composition is heated to a temperature substantially equal to the foaming temperature of the thermoplastic particles in the presence of the unfoamed resin particles in the producing process of the explosive charge. However, since heating was usually unrequired in the manufacture of slurry explosives, resin foaming in the producing process had little practical significance. Further, even if foaming by heating in the producing process was necessary, as understood from the explanation in JP-A-54-92614, there has been no alternative but to employ a two-stage system in which, for the reason of safety, a sensitizer is mixed after foaming by heating at the stage not yet added with the sensitizer has been completed.
In these hydrous explosives, delicate adjustment of the explosive components and the gel or emulsion structure is necessary for maintaining the detonation performance without containing a highly sensitive agent like nitroglycerin in dynamite, and a high-level technique is required for such adjustment. Thus, in the manufacture of said hydrous explosives, since the explosive detonation was affected by the quality and behavior of the explosive components through the forming process of the structure, a great deal of time and labor have been required for the control of quality of the starting materials and/or the control of the explosive producing conditions. As a result, there would arise the serious problems such as frequent production of the explosives of poor quality, which are unable to endure storage, and excessive deterioration of detonation performance with time. Especially when the amount of the chemical foams or the foaming agent used for the adjustment of density of the explosive composition is increased, it not only becomes harder to obtain the intended initial performance of the explosive but also the problem of deterioration of detonation performance with time becomes even more serious.
Further, the slurry explosives have their peculiar gel elasticity and lack plasticity, and when they are packed into a cartridge, such a cartridge itself proves to be soft and limp, so that it is hard to handle and also difficulties are encountered in inserting the cartridge into a blast hole, resulting in a reduced working efficiency for blasting operation. Also, because of poor moldability of this type of explosives, it was hard to use the explosives in the bare form without cartridge.
In the case of emulsion explosives, when they are given a sudden pressure, the emulsion structure could be destroyed to lose their detonating function (this phenomenon is called dead pressing phenomenon), and in short-delay blasting which is a normal form of blasting operation, there would be left an unexploded residue, posing a difficult problem for disposal thereof.